2002-09-04 04:00:00 PDT Washington -- Former Environmental Protection Agency administrator Carol Browner and Sen. John Edwards, D-N.C., joined forces Tuesday to try to block a Bush administration proposal to amend a key provision of the Clean Air Act.

Browner told a Senate subcommittee hearing that the agency she headed for eight years was on the verge of making changes to the Clean Air Act that would make the air "dirtier."

The plan, she said, "abandons the promise of the Clean Air Act -- steady air-quality improvements."

Edwards, chairman of the Senate Health, Education and Labor subcommittee on public health, contended that the changes would be bad for public health and added: "My intention is to do everything in my power to stop it."

Browner and Edwards were targeting an administration plan to give older coal-fired power plants more leeway to repair and expand facilities without triggering the Clean Air Act's "New Source Review" provision, which would require them to install modern pollution-control devices.

The act, passed in 1970, exempted existing power plants from many of its mandates. But under the New Source Review provision, it requires plants, including older ones, to install modern pollution-control devices if the plants are modified in any way that increases pollution levels.

EPA officials, who are awaiting final White House approval of their plan, dispute the contention that pollution levels will increase.

"We believe the changes we are making will have a positive impact on air quality," Jeffrey R. Holmstead, the EPA assistant administrator for air pollution programs, told the subcommittee.

Holmstead said the proof comes from a health assessment done in 1996, when the Clinton administration proposed its own amendments to the program. That assessment determined that the proposed changes would have no impact on the environment.

Browner called the 1996 assessment outdated, saying that it predates important scientific studies.

Scientists now estimate that as many as 30,000 Americans die prematurely each year from fine particulate pollution, which causes heart and lung disease.